Field of the Invention
The invention relates to instrument holders and methods for inspection of a dynamo-electric machine and dynamo-electric machines having the instrument holder, including a stator with a ferromagnetic yoke, a rotor being disposed in an internal recess of the yoke leaving a gap between the stator and the rotor, and instruments being introduced into the gap between the stator and the rotor for carrying out the inspection.
Assuring malfunction-free operation of an industrial dynamo-electric machine, particularly a turbo generator, and ascertaining any incipient malfunction of such a machine early, requires regular inspection of machine components that are repeated at intervals of from several months to several years, in which many kinds of examinations and tests must always be performed. One possible test is the visual inspection of the correspondingly accessible surfaces of the components of the machine, particularly the surfaces of the stator and the rotor. Other possible tests include inspecting the components by means of ultrasound using various methods, and checking the magnetizability of the yoke (which includes laminated metal plates in a stator) that is present in any dynamo-electric machine. In the case of such a test, the effect of a weak and locally limited magnetic field upon the yoke can, for instance, be determined and evaluated. Finally, mechanical tests should also be carried out, particularly strength tests and tests for any possible cracks. Last but not least, it is desirable to have the capability of rescuing smaller parts, such as loose screws or the like, from the machine.
The usual methods for inspecting a dynamo-electric machine require the removal of the rotatable part or rotor, which particularly in the case of industrial dynamo-electric machines, with electrical power outputs of several hundred MVA, is extremely time-consuming and expensive.
In order to enable such expensive dismantling work to be dispensed with if possible, an apparatus is known that permits pulling an instrument platform through the gap between the stator and the rotor of an industrial dynamo-electric machine (this gap is typically called an "air gap", regardless of the coolant system installed in the machine). The instrument platform runs on guide rails that extend from one end of the industrial machine to the other through the gap.
In an apparatus for inspecting tubes which is known from U.S. Pat. No. 4,255,762, a sensor with an optical inspection system is introduced on a support arm into the tube to be inspected. Such an apparatus is only usable in dynamo-electric machines with limitations, because in such machines the gaps to be inspected are often several meters long, with gap heights of only a few centimeters. It is virtually impossible to use support arms of such a length without vibration and without touching the stator or the rotor, so that adopting this known application to the inspection of dynamo-electric machines is not practicable.
U.S. Pat. No. 2,596,322 relates to a self-propelled carrier for welding or cutting tools for machining tubes. The carrier has wheels with built-in magnets in order to firmly hold the carrier on a tube to be machined. As intended, the carrier is supposed to circumvent the tube circumferentially and in so doing make a straight or oblique cut or carry out a welding operation.
U.S. Pat. Nos. 4,889,000, 4,970,890 and 5,105,658 relate to a system for inspecting a generator. The system includes a self-propelled device that can travel through a gap between a stator and a rotor of the generator. The device carries various means for inspecting the generator and is connected with a control and evaluation device for carrying out the inspection.